This specification relates to machining blades, bladed disks, blisks and aerofoils, such as integrally bladed rotors or stators for turbine engines.
Blades are traditionally machined in large sections, one side at a time or in multiple levels, all of which have the sole purpose of providing supporting material to reduce vibration during the machining process. The machining process for a blade typically involves three separate process steps: (1) roughing out the blade, (2) performing a semi-finishing process on the blade, and (3) performing a final finishing process to get the final desired blade shape. The manufacturing costs of such traditional machining processes can be relatively high due to the time needed to perform the separate process steps of the machining process and the tool wear caused thereby.
In addition, when the final blade is thin (as is common for aerofoils) the material being machined gets sequentially thinner in each separate processing step. This means that the part being manufactured becomes less strong and more subject to distortion during the machining process. This can lead to inaccuracies and poor surface finish in the final product. In order to address this issue, some have employed a roughing out process that creates a terraced support structure to provide additional strength to the part for the subsequent semi-finishing and finishing processes.
FIGS. 2A-2B show an example of a terraced support structure created by a traditional Computer Numerical Control (CNC) milling process. After the initial process step of roughing out a blade 200, the blade 200 includes both the stock material 210, 212 left after the roughing operation, and also the finished desired blade form 220, which is still to be revealed in the CNC milling process. As shown in FIG. 2A, the material left on a component being created forms a support structure that is terraced in shape.
This terraced shape has two disadvantages: first, the non-uniform shape of the stock material 210, 212 has inherent weaknesses, and second, the non-uniform shape of the material means the milling cutter encounters uneven amounts of stock material that can lead to tool damage, wear and push off, leaving excess material on the component. FIG. 2B shows a larger view of a portion 230 that includes rough stock material of the blade 200 from FIG. 2A. As shown, extra stock material 240 is encountered by a cutting tool 250 when traditional terraced stock methods are used in a CNC process.